Automatically controlled torpedo



Oct. 1, 1963 A D. B. HARRIS 3,105,452

AUTOMATICALLY CONTROLLED TORPEDO Filed Sept. 8, 1955 5 Sheets-Sheet 1 Invenlor DONALD B. HARR/S MMM/4.

lnvenfor D. B. HARRIS AUTOMATICALLY CONTROL-.LED TORPEDO 3 Sheets-Sheet 2 Oct. 1, 1963 Filed sept. 8, 1955 Oct. l1, 1963 D. B. HARRIS AUTOMATICALLY CONTROLLED TORPEDO 3 Sheets-Sheet 3 Filed Sept. 8, 1955v ME b TM Iv Inventor DONALD B. HARR/S horney MMF. Lw bm a UnitedStates Patent() 3,105,452 AUTOMATICALLY CONTROLLED TORPEDO Donald B. Harris, 1810 Middlefield Road,

Palo Alto, Calif. Filed Sept. 8, 1955, Ser. No. 533,163l 4 Claims. (Cl. 114-23) This invention relates to marine torpedoes, and more particularly relates to automatically controlled and directed marine torpedoes used in naval warfare to attack `enemy vessels. `It has particular application in use against enemy submarines, but may also be used against surface vessels.

The present application is a continuation-in-part of my copending patent application Serial No. 491,616, iiled lune 21, 1943, and entitled Electronic Control System for Directing a Torpedo at a Target.

Present methods of combating submarine attack depend principally on the use of depth charges dropped in the vicinity of the submarine by escort vessels. Results are unreliable, because the escort vessel is seldom in the vicinity of the submarine at the time when the submarines presence becomes lenown, either through its rising to the surface or showing its periscope preparatory to lining its torpedoes. By the time the Aescort vessel reaches the approximate location where the submarine was seen, the submarine has submerged, and may already be some distance away. Depth charges dropped under `these conditions may be relatively close to the submarine, but still not close enough to score a hit.

InV accordance with the present invention, a soundcontrolled torpedo is provided, for use by the escort vessel in a manner similar'to that now accorded depth bomb charges. A number of these `torpedoesare carried by the escort vessel, which follows the present practice of reaching the approximate location where the submarine was last seen, as soo-n as possible after it has submerged. The escort vessel then fires a torpedo, which sends out a sound :signal through theV water. This sound signal, propagated in all directions except vertically from the torpedo, is reilected from the hull of the submarine back to the torpedo. A control system which is provided in the torpedo responds to this reiiected sound signal and actuates a mechanism which at-al-l times keeps the horizontal and vertical rudders of the torpedo so disposed that in its course, the torpedo will remain pointed directly at the source of the reflected sound wave; or in other words at the submarine. The torpedo is, of course, equipped with the usual motors and propellers for propelling it forward, tand with the usual explosive charges; it accordingly follows its course in the direction of the reflected sound wave until it meets the submarine and explodes.

rial attenuating the reflection to a point where it will not act on the control system of the torpedo; A combination of these expedients may be employed. A time-delay is also provided which renders the control system inactive until, after the tiring of the torpedo, it has traveled out of the sound range of the escort vessel and arrived in the vicinity of the target. v y Incarrying out this invention, I employ two independent control systems; one which actuates the vertical rudder of the torpedo, and one which actuates the horizontal rudder of the torpedo. Each control system is provided with two microphones, nigidly attached to the torpedo.

amant ice.

A sound signal is generated locally in the torpedo by means of a high frequency oscillator and loudspeaker unit. This sound signal is intermittently interrupted by an interrupter. During the periods when the sound signal is being sent out, the microphone system is disabled, so that it will not respond to sounds emitted directly by the loudspeaker. When the oscillator is interrupted by the interrupter however, thereby stopping the emission of the sound signal, the microphone system is enabled by the interrupter. The reilected sound wave is received by one microphone, which converts the -sound wave to an electrical wave and impresses it on a modulator. A local tone signal generator or low frequency oscillator, separate and distinct from the oscillatorV and loudspeaker referred to above, is used to generate a signal also impressed on the modulator. Through the action of the modulator, the sound wave received by the iirst microphone is modulated by this signal. The modulated microphone signal is in turn combined with the .signalfrom the second microphone, which also receives the reflected sound wave and the result is introduced to an amplifier tuned tothe frequency of the reflected sound wave. The output of this amplifier is impressed on a detector .or demodulator,v

which derives from the complex wave a wave having a frequency equalto the frequency of the signal produced by the local tone signal generator in the torpedo and a phase relation dependent on the ,direction from which the reflected sound wave was received by the microphone system. This control wave is impressed on a system of thermionic tubes and relays arranged for reversibly operatinga motor mechanically coupledwith one of the rudders of the torpedo, either vertical or horizontal. This motor will operate either in a clockwise or counterclockwise direction, depending on the phase relation of the control wave, which as detailed above, in turn depends on the direction from which the reilected sound wave was received.

The rudders of the torpedo are accordingly moved in such directions that the torpedo tends to turn into line with the direction from which the reflected sound wave approached the torpedo. actly at the source Aof the reflected sound wave, the level of the control wave falls below a predetermined amplitude, or to Zero, bringing the motor drives to a stop', and holding the torpedo on a cour-se directed at the target.

Means are provided in the torpedo for taking advantage of the Doppler shift of the reflected signal to reject echoes received from stationary targets, such as reverberating strata the water, thus enhancing the sensitivity of the equipment to true echoes reflected from moving targets such as enemy vessels.

VThe advantages of this sound-controlled torpedo over conventional methods Vof attack in warfare against submarines will now be readily apparent. It is only necessaryfor the escort vessel to drop a torpedo in the general vicinity of the submarine 'whereupon the torpedowill automatically direct itself against the submarine,` and will follow this course until the target has been reached. Moreover, any attempts of the submarine to evade the missile will be unsuccessful, as the torpedo automatically changes its course to follow any change in course made by the submarine. Quick 'dives made by the submarine will also be inetiective, as the torpedo is arranged to follow the target not only in azimuth, but `also in depth. The necessity encountered under present systems, of gauging not only the location of the submarine in a horizontal plane, but also its depth, in order to set the depth charges Y properly, is therefore obviated.

When the torpedo points extorpedo which directs itself automatically at the target in response to a sound wave generated in the torpedo and reiiected from the target.

A further object of the invention is to provide a torpedo which will automatically follow the target, while i-n action, and will change its own course to match that of the target.

A further yobject of the invention is to provide a lsound-controlled, automatically-directed marine torpedo equipped with a control system adapted to respond accurately to thereected `sound signals throughout a range lof 360 degrees, without bi-directional ambiguity, and to keep the microphones of the system `so disposed als to be operating at their null point throughout the course of the torpedo.

It is a further object of the invention to provide an automatically controlled marine torpedo equipped with a control system responsive to a signal reected or transmitted from the target, and coupled to driving motors controlling the course of the torpedo, in such a way as to keep the torpedo directed at the target.

A further object of the invention is to provide a marine torpedo equipped with a means for generating a sound signal propagated toward 4the target, and with means for responding to the reflection of this sound signal from the target in order to direct the torpedo at the target.

A further object of the invention is to provide a marine torpedo adapted to follow a signal reflected from the target, and to ignore reflections of the same signal from the hulls of friendly vessels.

The foregoing and other objects of my invention will be best understood from the Ifollowing description of exemplifcations thereof illustrated in the accompanying drawings, in which:

FIG. 1 is a schematic mechanical and electrical block diagram of the components of the control systems of my invention;

FIG. 2 is a schematic electrical circuit diagram of a control system embodying the principles of the present invention;

FG. 3 contains graphs and diagrams illustrating the mathematical analysis of the control `system treated under the heading Theoretical Consideration of the Control System; the same including Sub-figures 3A (Microphone Input System), 3B (Wave Front Orientation), 3C (Graph of Sound Wave), 3D (Wave Forms in the Relay Control Tube System); and

FIG. 4 is `a diagrammatic cross-sectional view of the forward portion of a torpedo embodying the teachings of the present invention and illustrating a pair of microphones A and R which occupy a common vertical plane `and which effect vertical control of the torpedo, and a pair of similar microphones (A and R) which occupy a common horizontal plane and effect lateral steering, each pair of related microphones (A and R) forming part of a separate `control system. This view also illustrates the loudspeakers 16 and 17 which are shown as occupying a common vertical plane.

FIG. 1 is an electrical block diagram illustrating the coaction of the components entering into the control system. Equipment for actuating either the vertical or the horizontal rudder is shown, together with the common equipment used for both horizontal and vertical rudders. The various classes of equipment are blocked olf from one another by dotted lines, and are identified as to their functions, the control channel foreither horizontal or vertical rudder being shown `at the bottom of the figure, and the common equipment in the center.

Interrupter is of the multi-vibrator type, and is vdesigned to generate pulses at the rate of two to five cycles per second. These pulses, which consist of a momentary. reduction of positive potential, are alternately applied to Vleads 11 and 12. At the moment when a pulse is being applied to lead 11, the potential on lead 12 remains uniformly high, and vice versa. Leads 11 and 12 are connected to control the cathode bias of the microphone amplifiers in the control channel, and of the high frequency amplifier in the common equipment channel, respectively. When `the potential on these leads is high, the amplifiers to which they are connected, are disabled; when the potential is low the amplifiers are enabled. Thus,vas the pulses are sent out by the interruptor, the amplifiers in the common equipment channel and in the control channel are alternately enabled, the control channel being disabled at any moment when the common equipment channel is enabled, and vice versa.

The tone emitted -by the torpedo originates with high frequency oscillator 13. The frequency generated by this oscillator must be high enough to permit adequate wave-interference effects in the microphone and loudspeaker channels, and it is also desirable that it shouldl be beyond the normal audible frequency range, in order to prevent discovery by the enemy of the method of operation of the control system; on the other hand however, it cannot be too high without making the dimensions of the loudspeaker and microphone systems prohibitively small. In my system I prefer to use Ia frequency of approximately 15,000 cycles, but it is understood that other frequencies may be used.

Oscillator 13, then, continuously operates at a frequency of 15,000 cycles during the period of operation of the, torpedo, and this frequency is impressed on the input of high frequency voltage amplifier 14. When amplifier 14 receives a pulse over lead 12, it is enabled, and ampliiies the 15,000 cycle signal, impressing it on the input of high frequency power amplifier 15. Amplifier 15 in turn amplilies the signal and delivers it to loudspeakers 16 and 17.

Loudspeakers 16 and 17 therefore, emit a pulse of the 15,000 cycle frequency having a duration of from .10 second to .25 second, which travels outward through the water. The two loudspeakers are arranged vertically, one above the other, are operated in phase, and are spaced one-half wave-length apart. Under these conditions, sound waves propagated horizontally from the loudspeakers sulfer no interference effects and are propagated with an amplitude equal to the sum of the amplitudes of the individual loudspeakers. Any sound wave propagated in a vertical directionfrom either speaker will however,A be exactly cancelled by the wave emitted vertically by the other speaker. This system therefore, propagates the 15,000 cycle signal outward horizontally from the torpedo, and also at an angle downward and upward, but it does not propagate the signal directly vertically upward nor vertically downwardly. This feature is provided in, order to avoid the effects of reflections of the sound wave either from the surface of the water or from the oceani, bottom. Such reflections, if they existed, might turn the torpedo either vertically upward to the surface or vertically downward to the bottom, depending upon the depth. Since the torpedo however, emits no wave vertically upward or vertically downward, it is not affected by these reflections.

Since the velocity of sound in sea water is approximately 1454 meters per second, the wave length of the 15,000 cycle signal is (l454-z-l5,000) meters, or .09693 meter, or 9.693 centimeters. The loudspeakers are therefore spaced vertically 9.693-z-2 centimeters, or 4.847 centimeters apart. The same effect can be obtained by disposing the loudspeakers horizontally one-half wave-length apart and oper-ating them degrees out of phase and other configurations of phase and separation will also produce the same result. It is therefore understood thatl my choice of one-half wave-length separation `and zero phase diiference is not to be construed as limiting my invention to these requirements.

The duration of the pulse of 15,000 cycle signal, which is of course, controlled by the frequency of the interrupt` ter, is dependent on the maximum distance from the target at which it is desired to launch the torpedo or to enable ithe control system. If this distance be represented by s, the total distance traveled by the sound Wave from the torpedo to the target and back again will` be 2s, and the time consumed in traveling this distance will be: i 2s to effect the enablenrent of the control system, at fa maximunr distance of 200 meters from the target, the transmission time of the soundwave will be seconds, or .275 second. The period of the interruptor l must be greater than .275 second, Iand in this oase 'would probably ,be chosen as` .300 second, corresponding to ya frequencyV of 3.333 cycles per second. As the duration of the 15,000 cycle pulse occupies one-half of :the period of the interrupter, the duration of this pulse vvill be in this case .15 second. Equation 2 shows that as the distance from lthe target becomes greater, the minimum period of the interruptor also becomes igreater. It is, of cou-rse, not necessary to change the period or frequency of the interrupter `each time the torpedo is launched. A period suitable -for @average battle conditions is selected, the interrupter is set at the corresponding frequency, and the torpedo is then launched within ther-ange Igiven by Equation 2 above or set iso that the control system Will start to function within this range.

, When the sound wave .emitted by the loudspeaker system, traveling outward :through the lwater, encounters the target, -it is reflected back to the torpedo. It is picked up by the microphones of the control channel. These microphones comprise a microphoneA and a microphone R. Microphones A and R are arranged on a `line at right angles to the axis ofrlength of the torpedo and are permanently `attached to the body of the torpedo. In the case of the -microphone system controlling the horizontal rudder :of the torpedo (that is, the rudder which moves thetorpedo about its vertical taxis) the `line joining the microphones is also horizontal, While for the microphones controlling the vertical rudder, the line is also vertical.

As in the case of the loudspeaker system, other contig* urations of phase relationship and orientation will produce similar results in the microphone system, ,and my choice of arranging the microphones at right angles to the axis of length of the torpedo is not to be construed as limiting my invent-ion to this requirement.

DueV to the Well-known phenomenon of the Doppler shift, the echo signal received by microphones A and R is not at the lsame frequency as `the signal emitted by yloudspeakers 16 and 17, unlessboth the torpedo and the target are stationary, a condition which idoes not prevail in practice. i Instead, the frequency ofthe received echo signal is given by the well-known relationship FE=FS (zo t In Equation 3 Vo is positive when the object is moving toward the source and Vs is positive when the source is moving toward the observer.

Analysis of Equation 3 shows that, under conditions encountered in the field, the Doppler shift may rbe ap preciably large. If, for example, it be assumed that the velocity V `of sound in sea water is 1,430 knots, that the frequency of the emitted signal is 15,000 c.p.s. and that lthe torpedo is traveling 'at a velocity of 14 knots toward a stationary target, the Doppler shift of the echo received from the target will Ibe about c.p.`s., and the echo frequently received will be about 15,1140 c.p.s. If, in addition, the target is also moving in the direction of the torpedo at a velocity of 8 knots,V the Doppler shift becomes about 220 c.p.s. and the Ifrequency of the received echo is about 15,220. On the other hand, if the tar-get is moving -avvay lfrom the torpedo at a velocity of 8 knots (-with respect ,to the water) the Doppler shift is only about 60 c.p.s. .and the received echo frequency is 15,0610! c.p.s.

Thus, the frequency of the echo signal received from the target may vary over a considerable range, dependling upon the relative velocities of the torpedo and the target.

In addition to echoes receive-d from the target, the torpedo also receives echoes from various other objects in the Water. In particular, it receives echoes from rever- `berating strata located in various directions and at various distances fro-n1 the torpedo. These reverberating echoes rare `a detriment to the proper operation of the torpedo, since they tend to mask the true echo signal received from the target. Their frequencies may cover la relatively Wide rrange, since they may come from strata located directly in front of the torpedo, :giving a ilarge positive Doppler shift; from strata located directly in k:back of the torpedo, giving ya large negative Doppler shift; or'from strata located alongside the torpedo, giving no Doppler shift. However, due to the directional pattern of the transmitting loudspeakers, only the reverberation echoes received from strata ahead of the .torpedo are important. These lechoes have lpositive Doppler shifts, which are, of course, the same as that kof any stationary object, and which may therefore be about 140 c.p.s. in the case of ya torpedo moving at a velocity of 14 knots, Igiving a received rever- |beration frequency of about 15,140 -c.p.s. y

Y By Way of summary, it may there-forebe said that'the useful `echo signals received by `a 14 knot torpedo operated with an emitted frequency of 15,000 c.p.s. mayrange in frequency from about 15,060 c.p.s. to about 15,220 c.p.s. The unwanted reverberation frequency is about 15,1140

c.p.s.

It is one of the objectives of the circuitry employed in this invention to eliminate the unwanted reverberation frequency, and Ito pass the Wanted echo signals. This result is brought about \by incorporating in the circuit a set of rejection lters tuned to the frequency of the unwanted reverberation, about 15,140 c.p.s. in the case of the example cited. rlJhese rejection filters, to be desoribcdhereafter, will also reject echoes from any 'otherV stationary objects; including the target, i-f it happens to be stationary. i

The Wave picked up ibynmicrophone 18 (A) is impressed on microphone input transformer 20; "This transformer is of ea highly eicient type provided with a light -iron core and especially designed to amplify the Wave 'with a minimum of phase distortion. Condenser 21 in conjunction with the secondary lWinding Lof transformer 20 provides an anti-resonant circuit having -a pass-'band extending from `about 15,060 c.p.s. tot about 15,220 c.p.s. in orderlto accept the useful echo signals from targets. The voltage of the Wave induced in the secondary winding is greatly enhancedby'this anti-resonant circuit, and impressed `on the input of high frequency microphone amplifier 22. At the same time, the'anti-resonant circuit suppresses Waves outside its passband which may enter the transformer, such as, for example, propeller noise from the escort vessel, and prevents the delivery of such frequencies to the microphone amplifier.

Transformer winding 20 and condenser 21 constitute the rejection filter, referred to previously, which rejects the reverberation frequency. This fil-ter is tuned to the reverberation frequency, 15,140 cps. in the case of a 14 knot torpedo, and has a narrow rejection-band, extending from about 15,120 c.p.s. to about 15,160 cps. Thus, signals in this frequency range, representing echoes from targets moving at velocities less `than about 2 knots, are absorbed in the rejection filter and are not delivered to the microphone amplifier, there-by enhancing the sensitivity `of the system.

Amplifier 22 lamplifies the target signal, and delivers it to modulator 23, where it is modulated by a low frequency signal derived from low frequency oscillator 24. This oscillator generates a frequency of approximately 100 cycles per second. The exact value of this frequency is not, however, critical, and other values may be used. Modulator 23 is of the balanced type, and With a 15,200 cps. echo signal the result -of the modulation process is the creation of two side-band frequencies of 15,100 cycles and 15,300 cycles, respectively, the sum and difference of the 15,200 Iand 100 cycle frequencies. The original carrier frequency, 15,200 cycles per second, is not transmitted through the modulator. Viewed diagrammatically, the effect of the modulation process is to create a modulation envelope of the carrier-suppressed type having a frequency of 100 cycles per second.

When the reflected sound signal reaches microphone R, it also creates an electrical signal, which is impressed by transformer 26 on high frequency microphone amplifier 28 `after pasing through the anti-resonant circuit provided by condenser 27 operating in conjunction with the secondary of transformer 26. 'I'he reverberation frequency is removed by filter 26, 27'. After amplification by amplifier 28, the signal passes into phase network 29, which alters its phase by approximately 90 degrees. If, therefore the signal produced at the output of reference microphone R was yof the nature of (M cos this same signal, after amplification and pasage through the phase network will appear as (+M sin 0).

The modulated signal from the microphone A and the unmodulated signal from microphone R are now irnpressed simultaneously on detector 30 in such a manner that `the voltages of the two signals are additive. rIlhe result of this process of addition is the creation of a modulation envelope in which the carrier phase and the amplitude are both functions of the angle of approach of the echo signal.

Detector 30 now demodulates this modulation envelope. It will be shown later in connection with the theoretical consideration of the control system that, after filtering off unwanted vdemodulation products, the useful result of this process of demodulation is to reproduce the original 100 cycle wave generated by oscillator 24, either in phase with the original signal or 180 degrees out of phase with it, depending on the direction Ifrom which the sound wave approached the microphone system. The output of the detector is impressed on low frequency voltage amplifier 31, which amplifies the 100 cycle signal rand delivers it to power amplifier 32. Amplifier 32 further amplifies the signal and delivers it to the relay control tube system 33.

The original 100 cycle frequency generated by oscillator 24 is also delivered to relay control tube system 33 after amplification by low frequency power amplifier 34. This relay control tube system is therefore subject to the effects of two 100 cycle signals, which are in phase if the original sound wave approached the microphone sylstem from one side of the perpendicular to the line joining the microphones, and 180 degrees 4out of phase if the sound wave approached from the other side of the perpendicular. Control system 33 is so constituted that if these two` signals are in phase the circuit to relay 35 will be completed, and

this relay will operate, closing .the circuit to motor 37, which will operate in a counterclockwise direction, rotating the rudder post and the rudder in a clockwise direction viewed from above. If, however, the two signals are 18() degrees out of phase, relay 36 operates, also closing the circuit to motor 37, but with opposite polarity. Motor 37 will then rotate in a clockwise direction, turning the rudder post and rudder in a counterclockwise direction viewed from above. In either case, the rotation of the rudder will be in such a direction that Ithe torpedo will be steered to turn into line with the direction from which the sound signal approached the torpedo. As the torpedo turns, the microphone system also turns, and when an orientation is reached such that the line joining the microphones is perpendicular to the direction of approach of the sound wave, the amplitude of the cycle signal reaching the relay control tube system through the modulator channel :drops to zero. The relay control tube system then ceases to energize the relays, which return to normal, and the motor is no longer energized, and ceases to rotate the rudder. Gear system 38 is coupled to the rudder through magnetic clutch 39. When the circuit to this clutch is opened, it uncouples the rudder from the gear assembly and motor, and the rudder returns to normal under the in-fuence of spring 41, which is held in post 42, attached to the framework of the torpedo. 'Ilhe vtorpedo will therefore continue its course along the line into which it has been turned, which is, of course, directed to the source of the reflected sound wave, or in other words at the target. Any deviation of the torpedo from this course, caused either by a change in the direction of the torpedo or of the target, will cause the system again to generate a control signal and turn the torpedo into line again.

FIGURE 2 is a schematic electrical circuit diagram, illustrating electrical details of important features comprising a practical automatic torpedo control system constructed in accordance with the principles of my present invention. In this drawing, the detailed electrical connections of the various functional units of the control system, as shown in block form in FIGURE 1, are delineated. ln each case the functional units retain the same identification and number as were used in FIGURE l except that new numbers, 360 and 361 have been assigned to relays 35 and 36.

Interrupter 10 is disclosed as a multi-vibrator circuit, in which extremely low frequency oscillations are generated through the medium of voltages fed back from the plate of triode tube 100 to the grid of triode tube 101 through condenser 102, and from the plate of tube 101 to the grid of tube 100 through condenser 103. The mode of operation of multi-vibrator circuits is well known and will not be described in detail here. The frequency of the oscillations is controlled by the value of condensers 102 and 103 and of resistances 104 and 105.

The multi-vibrator interrupter 10, controls the operation of the sending and receiving channels of the control system in the following manner:

One characteristic of multi-vibrator circuits is that the two tubes alternately draw plate current, at a relatively steady value, and are suddenly forced to a cut-off condition, in which no plate current is drawn. Thus, while tube 100 is drawing plate current, tube 101 will be cut off. 'Ihis condition will exist, for the frequency previously set up, for about .15 second. During this period, current flows from the B supply through resistance `107, the space current path in tube 100, land cathode resistor `112, to ground. The current flow through resistor 107 causes a potential drop, so that the voltage at the junction between resistors 107 land 108` is less than the voltage of the B supply. The voltage at the junction between resistors 107 and 108 causes current to flow through resistors 108 and 111 to ground, setting up a potential drop across resistor 111. This potential drop directly supplies the cathode bias of amplifier tubes 115 and 1,16, in the microphone circuits of the interrupter, 4the voltage set up across resistor 111 of tube 101 i-s nearly equal to the voltage of the B supply, v

`and this voltage causes an extremely high voltage to be set up across 'resisto-r 110. This voltage directly provides i the cathode bias of tube 117 int-he loudspeaker amplifier,

and under these conditions `the grid bias of tube 1-17 is placed beyond cutoff, disabling the loudspeaker amplifier, and preventing the emission of the loudspeaker signal.

At the expiration of the `.l5 secon-d interval, tube 100 suddenly is placed beyond cut-off, through the multi-v vibrator action, and ceases to draw plate current. The voltage at the junction between resistors 107 and 1018' rises nearly to the voltage ofthe B supply, .and similarly, the voltage across resistor i111 rises to a high value, raising the grid bias of tubes 115 and 116 beyond the cutoff point, and disabling the microphone systems.

Also at the expiration of the second interval tube 101 suddenly starts to draw plate current, due to the multivibrator action. 'The voltage drop across` resistor 106 lowers the voltage at the junction between resistors 106 and 109, the voltage drop across resistor 11,0 is also lowered, the grid bias of tube 117 is reduced within the operating range of the tube, and amplifier 14 is placed in condition to amplify signals from oscillator 13, and transinit them to the loudspeakers, through amplifier 15. The torpe-do thereupon emits a Asignal which persists for approximately .l5 second, until the multi-Vibrator action suddenly causes tube 100 to start drawing current again, and tube 101 to cease drawing current, ire-establishing the ori-ginal condition. The cycle is then repeated, and continues to be repeated, las long as the interruptor continues to function.

vOscillator 13 is of the conventional feedaback type, tune-d to`15,000 cycles by means of condenser 119, con-v nected across the primary of transformer 120, which delivers the output of the oscillator tube 118 to Icube 117 in the high Vfrequency voltage' amplifier |14.

'Tube 117 is in turn coupled to power amplifier 15 by transformer 121. Power amplifier 15 is of the push-pull type containing triode tubes 1122 and 123. This type of amplifier is employed in order to permit emission of the purest possible tone signal, and at the highest possible level. Amplifier 15 is also tuned to the 15,000 cycle frequency in order to suppress undesirable harmonics. F[This tuning is accomplished by the resonant circuit provided by condenser 124, shunted across the secondary winding of transformer 121. i i v i Loudspeakers 16 and 17 may be of the permanent magnet type, as shown, or maybe of the type equipped with electrically energized fields. The output of power ampliiier 15 is delivered 'to the loudspeakers through output transformer 125.

Microphones A and R may be of any type, crystal, dynamic, ribbon, etc. High frequency microphone amplifiers 28 and 22 consistv of pentode tubes 115 and 116 equipped with volume control potentiometers 126 and 127. These potentiometers are employed to adjust the signals from microphones A and R to their proper relative values.

The output of tube. 116 in `amplifier 22 is delivered to modulator 23 by transformer 128,the secondary Winding of Vwhich is tuned for a pass-band from 15,060 c.p.s. to 15,220 c.p.s. by condenser 129. `This second tuned circuit increases the selectivity of `the control channel, and further suppresses any extraneousrfrequencies which may be picked up'. l Rejection .filter 12S', 132 further suppresses the reverberation frequency. Filter 20' 21 is tuned Vto the 10 reverberation frequency, 15,140 c.p.s., and rejects this frequency in the well-known manner of rejection filters.

Condenser 21 is made variable in order to permit theA filter to be tuned to the actual reverberation frequency encountered which may be different than 15,140 c.p.s. depending upon the speed of the torpedo.

Modulator 23 is of the balanced type, consisting of triode tubes 130 and 131. The echo signal is impressed on the grids of the modulator tubes in parallel, through condensers 132 and 133. These condensers are of relatively small capacity, so that they exert a minimum of shunting effect on the low frequency signal also impressed on the modulator from oscillator 24. They are of'suciently largecapacity, however, to present a low reactance to the high echo signal delivered by the microphone system.

Tubes 130 and 131 -in the modulator are maintained at 4 a high normal grid bias by means of cathode resistor 134,

which interposes a high value of resistance in the plate .current path, and which therefore maintains a high volt age between the cathode and the grid. This grid bias is sufficiently high so that when the tubes are not excited, they operate close to the cut-off point, and little plate currentflows. When the grids of tubes 130 and 131are excited in phase by the echo signal, in the absence of any excitation from oscillator 24, successive half cycles of the exciting signal alternately raise the potentials of both grids simultaneously above the cut-off point and lower the potentials of both grids simultaneously below the cutoff point. The potentials of the plates of the tubes similarly rise and fall together, in such a manner that the potential on the two ends or the primary winding of transformer 135 is always equal, no current ows through the transformer, and the Vexcitingsignal is not transmitted to detector 30. If, however, the two grids are also excited 180 degrees out of phase by the 100 cycle signal derived from oscillator 2K1, then during the half cycles of the 100 cycle signal which impress a positive voltage on tube 130, the bias of tube 130 is raised above the cut-off point, and the echo time, the cycle signal impresses a negative voltage on the grid of tube 131, causing its bias to become even more negative, forcing the tube definitely beyond the cutolf point, and disabling it so that the echo signal does not appear at the plate of tube 131. Under these condtions, the echo signal in tube 130, not being opposed by a similar signal in tube 131, flows through the upper half of the primary of transformer 135,k to the -B supply terminal. Due to the normal transformer action, a similar signal is generated in the secondary winding and impressed on the detector circuit 30.

Y Similarly, during the half cycles of the 100 cycle signal which impress a positivevoltage on tube 131, the bias of tube 131 is raised above cut-off, permitting it to pass the echo signal through to the plate circuit, while at the same time tube is forced beyond cut-off by negative voltage received by its grid from the 100 cycle signal, disabling the tube. '.llhe echo signal then flows from the lower terminal of transformer 135 through the primary winding to the B supply terminal, causing a similar signal tovappear on the secondary winding. v

Modulation of the carrier suppressed type is thus eectuated. The useful result of this process, as will be demonstrated mathematically later, yis to multiply the amplitudes of the echo signal and the 100 cycle signal together, so that the output contains [N cos (6H-u) sin where cos (0-j-u) represents the instantaneous value of the echo signal, yand sin p represents the instantaneous value of the 100 cycle signal. Thus the amplitude ofthe 100 cycle signal directly controls the amplitude of the echo signal appearing in theroutput, which starts at zero. amplitude, rises to maximum amplitude, and falls back to zero amplitude again during each half cycle of the 100 cycle signal.

The modulated echo signal is vnow delivered to detector 30 by transformer `135. yIn detector 30, the modulated signal is first mixed with the unmodulated signal derived frompmicrophone R after it has been amplified by amplifier 28. This amplifier' consists of a resistance coupled pentode tube, 115, and embodies tuned circuit 26, 27 and rejection filter 26', 27 designed, respectively, to accept echo signals in the band from 15,060 to 15,220 c.p.s., and to reject the 15,140 c.p.s. reverberation frequency. The output of amplifier 28 is delivered to detector 30 through phase network 29. This network consists of a series resonant circuit, including condenser 136 and inductance 137. 'llhis circuit is tuned to the echo signal, under which conditions, as is well known in resonant circuits, the reactance of the circuit drops to zero, and the combination of the condenser and inductance offers a purely resistive impedance to the fiow of current. Therefore, the current through the network is in phase with the voltage appearing on the plate of tube 115, the instantaneous value of which, is a linear function of (cos since it is derived from the reference microphone. The current through the network after reversal of phase in the amplifier, is therefore also a linear function of (-cos 6). As is will known, however, the current through an inductance lags behind the voltage across the inductance by an angle of 90 degrees. The voltage across the inductance therefore leads the current by 90 degrees, and is alinear function of (+sin 0). This voltage is delivered to detector 30 in series with the secondary of transformer 135, so that the voltage in the transformer is added to the voltage across inductance 137.

Detector 30 now rectifies the modulation envelope, reproducing an unmodulated l0() cycle frequency either in phase with the original oscillator 24 signal or 180 degrees out of phase with it depending on the direction from which the sound signal approached.

The secondary winding of transformer 135 is tuned to the echo signal frequency by means of condenser 138, in order to further suppress extraneous signals. Rejection filter 135', 138 further suppresses the reverberation frequency received both from the A and from the R channels. The rectified signal delivered by diode detector tube 139 appears across resistance 140, which is shunted by condenser 141 in order to provide a path for absorbing the residue of the echo signal.

The 100 cycle signal appearing across resistance 140 is delivered to amplifier 31 through condenser 141:1, and potentiometer 142, which is employed to adjust the level of the 100 cycle signal to match properly the 100 cycle signal delivered directly to the relay control tube system by oscillator 24. Amplifier 31 contains pentode tube 143, which is coupled -to low frequency power amplifier 32 by means of resistance coupling, consisting of plate supply resistor 144, condenser 145 and grid resistor 146. Amplifier 32 contains triode tube 149, designed to develop power, and a phase correcting network consisting of resistor 147 and condenser 148. This phase correcting network performs the function of correcting any phase distortion which may have taken place in amplifiers 31 and 32, in detector 36, or which may occur in the input circuit of the relay control tube system, in order to assure that the amplified 100 cycle signal from amplifier 32 will be in phase, or 180 degrees out of phase, in the relay control tube system, with the 100 cycle signal delivered to the relay control tube system directly by oscillator 24.

The output of amplifier 3.2` is coupled into relay control tube system 33 by transformer 150. The secondary of transformer 150 is tuned to 100 cycles by condenser 151. The 100 cycle signal is impressed in parallel on elements 152 and 153 of tubes .158 and 159 in the control system, through resistances 160i and 161, and in series with a positive bias derived from the B supply through resistors 162 and 163, with resistor 164 in shunt to ground. Resistor 246 is used to adjust the amplitude `of the 100 cycle signal impressed on elements `152 and 153, and the relative values of resistors 162, 163, and 164 determine the value of the bias on these elements.

The lOO cycle signal lfrom oscillator 24 is also impressed on elements 156 and 157 of tubes 158 and 159, after passing through low frequency amplifier 34. The signal from amplifier 34 is impressed `on elements '156 and 157, 18() degrees out of phase, in series with the windings of relays 360 and 361, which are shunted by condensers 362 and 363. The signal is delivered from amplifier 34 through transformer 364, which is of the step-down type, and which is shunted 'by resistor 330 and condenser 331 to assure good voltage regulation under conditions when tubes 158 and 159 are drawing current. Amplifier 34 is a push-pull amplifier equipped with beam-power tubes and 166, designed to give large power output. It is resistance-coupled from oscillator 24 by means of centertapped resistor 167 and condensers 168 and 169. Oscillator 24 contains triode tubes 170 and 171, which produce oscillations by means of energy fed back from the plate of tube 170 to the grid of tube 171 through condenser 172 and from the plate :of tube 171 to the grid of tube 179 through condenser 173. Grid resistors 174 and 175 are provided with taps, from which the 100 cycle signal voltage is fed to the control channel, through condensers 176 and 177. The oscillator is tuned by the resonant circuit consisting of condenser 178 and. centertapped inductance 179, which also serves as the plate supply feed for the Ioscillator tubes. The B supply for the oscillator and the relay control tube system is maintained at a constant voltage, in order to improve the reliability and accuracy of the control system, by the interaction of condenser 180, resistor 181, and voltage control tube 182. This tube is rated to maintain a voltage of 150 volts at point 183. An increase in the voltage supply to point 183 causes additional current to iiow through tube 182, increasing the potential drop across resistor 181, and maintaining the voltage at point 183 constant in the well-known manner of voltage regulators.

The relay control tube system 33 operates in the following manner:

Tubes 153 and 159 may be thigh vacuum triodes, mercury vapor relay tubes or Thyratrons, or cold cathode glow-discharge tubes with a starter-anode. The tubes illustrated are the latter type and are known currently as type @A4-G. They are designed so that av voltage of 110 volts at starter-anodes 152 and 153 will fire, or break down the tube affected and establish a current iiow between anodes 156, y157 and cathodes 154, 155. The initial positive bias on starter anodes 152 and 153 is of the order of 85 volts to ground. Cathodes 154 and 155 are normally maintained iat a positive 12 volt potential 'with respect to ground, through cathode resistors 184 and 185 connected to battery through relay armatures 186 and 187. The relative potential of `starter anodes 152 and 153 with respect to anodes 156 and 157, which are grounded, is 85 volts, and the relative potential of starter anodes 152 and 153 with respect to cathodes Y154 and 155 is 8,5 minus l2, or 73 volts.

Transformer 364 continuously impresses a voltage of approximately l5() volts to ground on anodes 156 and 157, as shown invcurves (2) and (3) respectively of FIGURE 3D. 'I'his voltage is the alternating peak voltage of the signal derived from oscillator 24. Since it is impressed 1810 degrees out of phase on the two tubes, and since it is either in phase with or out of phase with the control signal impressed in phase on starter anodes 152 and 153, as shown in curve (1) of FIGURE 3D, either starter anode 152 will 'be in phase with anode '156, or starter anode 153 will be in phase with anode 157. However, if the elements `of tube 158 are in phase, the elements of tube 159 will be out of phase. By in phase is meant that the two elements are positive with respect to ground at the same moment, yand negative with respect to ground at the same moment.

When the control signal impressed on elements 152 and 153 reaches a value of approximately 30 volts, the

1? :total voltage of the starter anodes with respect to ground reaches 115 Volts, placing both tubes in condition to lire. Only the tube however, in which the starter anode and the anode are in phase, will break down, because in the other tube the anode will be negative at the moment when the star-ter anode is positive, and the anode will therefore not be in a condition to draw current, even though the starter anode has placed Ithe tube in condition totire.

Now, if the control signal derived from the control channel is in phase with the signal from the oscillator the circuit is so connected that tube 158 will `have its elements in phase. Under these conditions, tub-e '153i will therefore tire as shown in curve (4) of FIGURE 3D. If, however, the two signals are 180 deg-rees out of phase, the

elements of tube 159 will be in phase, and tube 159 will tire, as shown in curve (5) of FIGURE 3D. The choice of the tube which tires is therefore dependenton the rel-a- .tive phase relationship of the two signals, and therefore on the direction from -which the original sound signal approached the torpedo.

-The tiring of the tube continues only during the half cycle when both elements are positive. When both elements Abecome negative on the succeeding half cycle the firing stops, to be resumed on the next positive half cycle. The control relay, however, pulls Iup and is energized during the positive half cycles, and the interval of time in the negative half cycles during which no current tlows is too short to `allow the relay .to fall back. The relay therefore operates and remains operated as long as the tube continues to lire on the positive half cycles.

The operation of eitherof the two control relays causes current to flow, from battery on the movable spring of the unoperated relay, through the motor and electromagnetic clutch in parallel, to ground on the stationary spring of the operated relay. The direction of current flow, however, and consequently the direction of rotation of the motor, depends on which ofthe two control relays is operated, and therefore on the direction from which the original sound signal approached the torpedo. The field of the motor is, of course, continuously energized in one direction; a reversal of the direction of current ow through the armature therefore causes the motor to reverse. y,

Relay 249 is a slow-acting rel-ay, preferably of the solenoid type equipped with a piston and cylinder known as a dash-po The contacts of this relay `are inserted in series Withthe motor circuit. When the torpedo is fired, relay 249 is momentarily energized, Ibreaking the circuit, and disabling the control system. It returns to normial slowly, and iinally closes the motor circuit after the torpedo, under the control of the conventional gyroscope, has passed out of the sound range of the escort vessel and into the vicinity of the target. 'Ihis feature is'provided as a safeguard against possible false bearings dueto reflections from .the escort vessels hull. `It may be employed optionally, and the relay may be set for any desired elapsed-time interval.

'Miscellaneous equipment inthe control channel, not previously described specifically in connection with either FIGURE 1 or FIGURE 2, includes:

Cathode `resistors, for maintaining proper bias conditions in various tubes, 214, 215, 216, 217 244, 247.

Cathode condensers, shunted, across cathode resistors to provide ya path for alternating currents in the cathode circuits, 220, 221, 222, 223, 224, 225, 226, V2.35, 245, 243.

Screen-grid supply resistors, in pentode tube circuits, 231, 2312, 234. i j

`Voltagedivider resistors, inserted in the modulator input circuits for the purpose of adjusting the level of th modulating voltage, 240, 241, 242, 243.

Variable resistor 2416, in the relay control tube system, used to adjust the Ileve-l of the incoming control signal, so thatit will maintain theproper relationship to the level of the signal derived directly from oscillator 24.

1d l Y T heor'etcal Consideration of the Control Systemi A simplitied schematic diagram of the microphone input circuits employed is shown in FIGURE 3A. Referring rst to the microphone system consisting of microphone A and transformer 20, the voltage delivered by this system to the input terminals of the high frequency microphone amplifier will be:

eSrNeA Where es is the instantaneous voltage impressed on the grid.

N is the turns ratio of the transformer.

eA is the instantaneous voltage across the primary of the transformer.

lEquation 1 assumes that the impedance presen-ted to the microphone by the primary winding of the transformer is nearly infinite, and that therefore the entire vol-tage developed by the microphone is impressed on the transformer. This is a condition easily approximated in practice.

Now, referring to `'FIGURE 3B, assume that .a sound wave, two successive troughs of which are represented by lines PQ and RS, 'approaches the microphone system along la line CD. The direction tof motion of the wave may be considered to be from IC to D, and the wave front makes an angle a with the li-ne joining the microphones. Assuming that Aat any given moment the electrical signal generated by microphone R has a Vol-tage:

eR=E cos 0 (2) Where E is the maximum lamplitude of the signal, and 0 is the phase angle of the signal.

The phase angle of the sound Wave may be also represented by 0, las demonstrated in the lgraph of FIGURE 3C, the vertical axis of which represents the yamplitude of the sound wave, and the horizontal axis of which represen-ts its phase angle. In this iigure, zero phase .angle is assumed to exist rat the moment when microphone R,

lthe location of which is indicated below the curve, is

eA=E cos (IH-u) (3) Where u is the angular phase difference existing in the wave between microphone A and the reference microphone R.

' Now, referring to FIGURE 3B, it is seen that the distance Ialong the line CD, perpendicular to the wave-front, between the part of the Wave affecting microphone A and the part of the wave affecting microphone R `at any given instant, is d/ 2. If the Wave-length of the signal is A, this distance d/ 2 represents -a Ifraction of a wavelength (vd/2)+}\ or d/2)\. As there are 211- radians in a complete wavelength, this salme distance, d/ 2, also represents an angular phase diiference equal to 2n' multiplied by the lfraction d/Z. This is the phase difference ul of Equation 3. Therefore, we have Now, the continuouslyrvarying phase angle, 6, is of course equal :to:

fiez-ff k(8) Where f is the frequency of the signal and t is the time. Substituting `(7) and (8) in (3) we obtain,

eA=E cos (21rfl-i-1rD sin a/A) (9) Then, returning to Equation 1, the voltage impressed on the grid of the microphone amplifier is seen to be:

1rD Sin a) It is desirable to employ a signal frequency as high as possible, in order to assure the secrecy of the method used. As the frequency becomes greater, however, the wave-length decreases, increasing the value of D for a given separation, in terms of wave-length. It can be shown that the frequency cannot be increased to a point where D has a value of one wavelength, or a lgreater value, because such values result in Zero values of the control signal yat points other than degrees, 180 degrees, etc. `It can also be shown, however, that for values of D only slightly less than one wave-length, such as D=.9 wave-length, the value of the `control signal remains negative during the rst two quadrants of rotation from =0 to o=180, and positive throughout fthe second two quadrants, from a=180 to et-=360. Values of D 4in excess of one-half wave-length, but less than one whole wave-length, may, therefore be used, since the :only requirement `for successful functioning of the system is that the control signal sha1-l be positive for one half of a full revolution and negative for the other half. A value of D equal to .9 wave-length has been selected for application in the practical embodiment of the control system.

It Iwill now be convenient for purposes of reckoning to transform `Equation 10 into the form of `Equation 3, eliminating the detailed expressions representing the two angles. Substituting back in Equation l0 the equivalent of (21rft) developed in Equation 8 and the equivalent of (1rD sin a/k) developed in Equation 7, Equation 10 becomes:

This voltage is now applied to fthe :grid of the microphone amplifier 22, is amplified by the 'amplifier 'and delivered to the modulator grids by the output transformer, through the series condensers in such a manner that the voltage appearing lon the modulator grids has the same value and sign on the grids of both tubes. If the voltage `gain produced by the amplifier, taking into account the circuit losses, be represented by k1, and it is assumed that the output transformer of the amplifier is connected to -avoid phase reversal, then the voltage applied to the modulator `grids will be:

At the same time, ra second alternating voltage generated by oscillator 24 is applied to the grids of the modulator in such `a manner that the gnid of one tube is always positive while the grid of the other tube is negative, and vice versa. This voltage may be represented as:

Where Et is the maximum amplitude of the oscillator voltage applied to the modulator grids, `and fg, is the frequency of the oscillator.

The net instantaneous alternating voltage applied to the grids of the tubes accordingly has thel following values:

For tube l eS=NE cos (21j/5+ (10) e1=e0+e/2 (14) For tube 2 e2=e0-e/2 (15) Now both modulator tubes are operated on a portion of their characteristic near the cut-off point. If it be lassumed that the characteristic curve in' this neighborhood is panabolic in form, then the relationship between the plate current `and grid voltage of either tube may he written as rfollows:

Substituting in Equation 17 the values of grid voltage obtained for the two tubes in Equations 14 and 15, we obtain, for the plate currents in the two tubes:

Since these currents flow in opposite directions through the output transformer they rnust be subtracted, to obtain the value of the voltage in the secondary of the transformer. Completing this process of subtraction, we obtain: (neglecting the `direct current components, which will not pass through the transformer):

Where:

ed is the linstantaneous voltage impressed on the detector k3 is a constant determined by the relation of the output transformer characteristics to the constants of the circuit. V

Substituting the original meanings of e0 land e6, as

defined in Equations 12 and 13, we obtain:

In' Equation 21, the first term represents the frequency of oscillator 24, and the second term represents the useful lcomponents of the modulated wave. The first term performs no useful function in the circuit, and it is desirable to suppress it. This suppression is brought about, in the practical embodiment of the control system by the tuned input circuits of the .diode detector, which responds only to the second term, and by keeping E, the amplitude of the control signal much larger than E, the amplitude of the oscillator signal. To `all intents and purposes, therefore, the directional voltage actually impressed on detector 3() may be represented by:

The signal of Equation 23 may be represented by a conventional modulation envelope of the carrier suppressed type.

The voltage represented by Equation 23 is now combined, in the `detector input circuit, with the voltage derived from the reference microphone. This voltage,

Where Rp is-theplate resistance of the amplifier tube and XL and XC are' the reactances of the inductance and 4condenser in fthe series resonant circuit into which the amplifier feeds. Since this circuit is resonant, XL=XC, (XL-Ireen, `and Y This current iiows through the inductance, and sets up a voltage across it:

The (-,j) in Equation 28 means that eL lags behind E cos Iby 90 degrees. Or:

k1X ARD If the constant in the above expression be represented by Kn the equation becomes:

L 6n- L E sm 0 en=KnE sin (30) The result of adding thesignal ed and the signal en in the detector input circuit is to create a signal -l-KnKd sin (21H-u) Sin fbi-Kali@ Siu t-w) sin 11 L@ 6) Y 7) y 5412-? cos 2+i2 eos 2(0-l-u) Y Note that in the foregoing expansion, successive equations are related on a line-by-line basis, for purposes of clarity. That is, for example, the terms on the rst line of yEquation 35 rare an expansion of theterm on the first yline of Equation 34, and so on. References tothe particular expansion processes used are not included, as they are conventional.

vIn Equation 37 the terms have the following significance;

Term (l) is D C., and is ltered out.

Term (2) is carrier frequency and is filtered out.

Term (3) is twice carrier frequency modulated by the low-frequency control signal, which produces sidebands close to the carrier, and is filtered out.

Term (4) is the use-ful remaining term after ltem'ng.

Term (5)V is D C. and is iiltered out.

Term (6) is twice the control signal frequency and is ltered out. Y

Term (7) is twice carrier frequency 'and is ltered out.

Term (8) is twice carrier frequency, modulated by a frequency Itwice that of the low-frequency control signal, and is filtered out.

Thus, the only term left in the output of the detector is term (4), and is the low-frequency control signal given by The frequency ofthe control signal is that of the local oscillator, fand the amplitude is seen to be dependent on sin u, which in turn is'dependent on the angle of rotation of the sound wave front. If the sound Wave frontis rotated less than degrees in a counterclockwise direction, sin u 4is negative, and the control signal becomes positive, or in other words, in phase with the original signal generated by oscillator 24,

On ythe other hand, if the sound wave front is rotated less than 180 degrees in 'a clockwise direction, sin u is positive, and the resulting value of the eC, the control signal, is negative: in other words, i-t is 180 degrees out of phase with the oscillator signal of Equation 39.

In either case, the amplitude of the control signal will depend on the absolute numerical value of sin u.

'Ihe control signal, after ampliiication, is now impressed on the tubes of the relay control tube system. The signal of Equation 39 is also impressed on the relay control tube system. As detailed in connection with [FIGURE 2, if the signal impressed directly by the oscillator, e, is in phase 'with the signal derived from the modulator, eC, Ithe control system is so constituted that theupper of the two tubes will break down, operating the upper relay, and turning the rudder in a clockrwise direction. This condition will prevail when sin u is negative, or in other words when the sound wave front has been rotated in a counterclockwise direction, equivalent to a clockwise rotation of the microphone system and the axis of the torpedo. The clockwise rotation of the rudder will, therefore, bring the course of the torpedo back to bear on the source of the reflected sound wave.

If, on -the contrary, e, is 180 degrees out of phase with Y eC the lower of the two tubes will break down, operating the lower relay, and turning the rudder in a counter-clockwise direction. This condition will prevail when sin u is positive, or, in other words, when the sound wave front has been rotated in a clockwise direction, equivalent to a counterclockwise rotation of the microphone system and the laxis of the torpedo. The counterclockwise rotation of the nudder in this case will, therefore, again bring the course of the torpedo to bear at the target. The operation of the relay control tube system is illustrated in FlG- URE 3D. The left hand section of this figure, entitled sin u negative (counterclockwise rotation of soundwave front) shows the condition when the control signal is in phase with the original oscillator signal. Under these conditions, the control signal impressed in phase on both tubes, as illustrated in curve (1), is seen to be in phase with the oscillator signal'impressed on tube 158, as shown in curve (2), but out of phase with the oscillator signal impressed on tube 1519, as shown in curve (3). Tube 158 therefore tires, during the irst half-cycle only when both elements of the tube are positive, but tube 159 does not fire, because during the entire cycle the two elements of the -tube maintain Vopposite polarity.

)On the other hand, if sin u is positive, as a result of a clockwise rotation of the sound-wave front, the condition will be as illustrated in the right-hand section of FIGURE 3D. Here it is seen that the control signal of curve (i1) yis in phase with the oscillator signal impressed on tube 159, but out of phase with the oscillator signal impressed on tube y158. Tube 159 therefore Itires, under these conditions, during the second half-cycle only. Tube `1'58, however does not lire.

I cl-aim:

1. A control system for automatically and positively directing a torpedo at the target in response to a sound signal proceeding from the target, comprising in the torpedo a pair of signal translating devices mounted in spaced relation on said torpedo, modulator and oscillator means for converting the signals of said signal translating devices into a control signal havingV a frequency identical with that of said oscillator means -and having a sense which is determined by the relative phases of the outputs of said signal translating devices, an electronic system responsive to said control signal, and an electromagnetic rudder control system actuated by said electronic sys-tem in accordance with the sense of said control signal.

2.` A control system for automatic-ally directing a torpedo at the target comprising in the torpedo a tone signal generator, apparatus for broadcasting the signal produced by the tone signal generator, a microphone system responsive directionally to echoes of said tone signal reflected from targets, rejection filters for rejecting echoes proceeding from stationary objects, by selecting and rejecting those frequencies characteristic of such objects, modulator and oscillator means for converting the signal of the microphone system into a control signal having a frequency identical with that of said oscillator means, said control signal having a phase which denotes the direction of said echoes, an electronic system responsive to said control signal, and an electro-magnetic rudder control system actuated by said electronic system in accordance with the phase of said control signal.

3. A control system for automatically directing a torpedo at the target in response to a sound signal proceeding from the target, comprising in the torpedo a rnicrophone system responsive directionally to sa-id sound signal, a phase shifting network for introducing a phase shift between the outputs of the elements of said microphone system, modulator -and oscillator means for converting the signal of the microphone system into a control signal having a frequency identical with that of said oscillator means, and having a phase which denotes the direction of the sound signal, an electronic system responsive to said control signal and an electromagnetic rudder control system actuated by said electronic system in accordance 'with the phase of said control signal.

4. A control system for lautomatically directing a torpedo at the target in response to a sound signal proceeding from the target, comprising in the torpedo amicrophone system, a phase shifting network for introducing a phase shift between the outputs of the elements of said microphone system, modulator and oscillator means for converting the signal of the microphone system, in conjunction `with said phase shifting network into a control signal having a frequency identical with that of said oscillator means, said control signal having a phase which denotes the direction of the sound signal, an electronic system responsive to said control signal and an electromagnetic rudder control system actuated by said electronic system in accordance with the phase of said control signal.

References Cited in the file of this patent UNITED STATES PATENTS 1,137,222 Leon Apr. 27, 1915 1,806,346 Hammond May 19, :1931 1,892,431 Hammond Dec. 27, 1932 2,077,401 `Crosby Apr. 20, 1937 2,109,475` 'Fanning Mar. 1, 1938 2,166,991 Guanella July 25, 1939 2,262,931 Guanella Nov. 18, 1941 2,349,370 Orner May 23, 1944 2,408,395 Hays Oct. 1, 1946 2,431,854 Wood Dec. 2, 1947 

1. A CONTROL SYSTEM FOR AUTOMATICALLY AND POSITIVELY DIRECTING A TORPEDO AT THE TARGET IN RESPONSE TO A SOUND SIGNAL PROCEEDING FROM THE TARGET, COMPRISING IN THE TORPEDO A PAIR OF SIGNAL TRANSLATING DEVICES MOUNTED IN SPACED RELATION ON SAID TORPEDO, MODULATOR AND OSCILLATOR MEANS FOR CONVERTING THE SIGNALS OF SAID SIGNAL TRANSLATING DEVICES INTO A CONTROL SIGNAL HAVING A FREQUENCY IDENTICAL WITH THAT OF SAID OSCILLATOR MEANS AND HAVING A SENSE WHICH IS DETERMINED BY THE RELATIVE PHASES OF THE OUTPUTS OF SAID SIGNAL TRANSLATING DEVICES, AN ELECTRONIC SYSTEM RESPONSIVE TO SAID CONTROL SIGNAL, AND AN ELECTROMAGNETIC RUDDER CONTROL SYSTEM ACTUATED BY SAID ELECTRONIC SYSTEM IN ACCORDANCE WITH THE SENSE OF SAID CONTROL SIGNAL. 